The present invention relates generally to implantable medical devices, and more particularly to an implantable device for detecting and monitoring the progression of congestive heart failure.
Many patients who have suffered one or more myocardial infarctions subsequently require treatment for congestive heart failure (CHF). The left heart fails while the pumping function of the right heart remains adequate, because the latter has only about 20% of the workload of the former. This leads to an increase in blood volume congested to the lungs, resulting in pulmonary congestion, build up of edema, and congestion of internal organs including the stomach and intestines. Increased fluid in the stomach and intestines reduce their ability to absorb drugs prescribed for treatment of CHF, particularly diuretics. The congestion is often accompanied by a worsening of myocardial function, with consequent drop in blood pressure and reduced renal perfusion, which only further aggravates the congestive situation. Thus, late recognition of congestion leads to increased dosages of oral diuretics that are unsuccessful to treat the condition, ultimately requiring that the patient be hospitalized.
Avoidance of hospitalization and the pitfalls of late treatment require detection of CHF at an early stage, so that the prescribed drugs can be fully absorbed and effective. If detected early, a combination of diuretics and other drugs can slow the progress of the disease and allow the patient to enjoy an improved lifestyle.
It is a principal aim of the present invention to provide an implantable heart failure monitor which is capable of achieving very early detection of CHF.
The implantable medical device of the present invention is of size smaller than a typical pacemaker devicexe2x80x94about the size of a thumb. It is implanted in a subcutaneous pocket formed by the surgeon in the patient""s chest, under local anesthesia and minimally invasive requirements. The device includes a hermetically sealed can with appropriate electronic circuitry inside. A set of can-mounted electrodes is used to measure the impedance of the adjacent tissue and most especially the lung tissue. The progressive retention of fluid in the lungs and congestion of the ventricle together result in a reduced impedance measurement that is monitored either continuously or periodically by the device.
In a preferred mode of operation, the device alerts the patient and the attending physician when a diagnostic threshold is reached which is indicative of the progression of CHF. The overall architecture of the device follows implantables practice, and is a stand-alone monitoring device. However, it should be appreciated that the partitioning of the device is flexible and the division of sensing and analysis structures can be shared between implanted and external (remote, i.e., non-implanted) devices. Conventional programming and telemetry links can be used to connect the implanted device to the remote device.
For example, the signal processing may be performed entirely internally within the device, or the device may operate as a data logger and communicate with an external programmer device which participates in data reduction and analysis.
Although specific structures are shown as being dedicated to specific tasks, it should be apparent that certain functions may be shared if the device is integrated with other diagnostic or therapeutic devices. For example, the electrode set used to determine the impedance of the lungs could be used for additional purposes.